Depositing tungsten into high aspect ratio features

ABSTRACT

Methods and apparatuses for filling high aspect ratio features with tungsten-containing materials in a substantially void-free manner are provided. In certain embodiments, the method involves depositing an initial layer of a tungsten-containing material followed by selectively removing a portion of the initial layer to form a remaining layer, which is differentially passivated along the depth of the high-aspect ration feature. In certain embodiments, the remaining layer is more passivated near the feature opening than inside the feature. The method may proceed with depositing an additional layer of the same or other material over the remaining layer. The deposition rate during this later deposition operation is slower near the feature opening than inside the features due to the differential passivation of the remaining layer. This deposition variation, in turn, may aid in preventing premature closing of the feature and facilitate filling of the feature in a substantially void free manner.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.13/016,656, entitled “DEPOSITING TUNGSTEN INTO HIGH ASPECT RATIOFEATURES” by CHANDRASHEKAR et al., filed on Jan. 28, 2011, whichapplication is a continuation-in-part of U.S. patent application Ser.No. 12/535,464, entitled “DEPOSITING TUNGSTEN INTO HIGH ASPECT RATIOFEATURES” by CHANDRASHEKAR et al., filed on Aug. 4, 2009. U.S. patentapplication Ser. No. 13/016,656 is also a continuation-in-part of U.S.patent application Ser. No. 12/833,823 entitled “DEPOSITING TUNGSTENINTO HIGH ASPECT RATIO FEATURES” by CHANDRASHEKAR et al., filed on Jul.9, 2010.

BACKGROUND

Deposition of tungsten-containing materials using chemical vapordeposition (CVD) techniques is an integral part of many semiconductorfabrication processes. These materials may be used for horizontalinterconnects, vias between adjacent metal layers, contacts betweenfirst metal layers and devices on the silicon substrate, and high aspectratio features. In a conventional deposition process, a substrate isheated to a predetermined process temperature in a deposition chamber,and a thin layer of tungsten-containing materials that serves as a seedor nucleation layer is deposited. Thereafter, the remainder of thetungsten-containing material (the bulk layer) is deposited on thenucleation layer. Conventionally, the tungsten-containing materials areformed by the reduction of tungsten hexafluoride (WF₆) with hydrogen(H₂). Tungsten-containing materials are deposited over an entire exposedsurface area of the substrate including features and a field region.

Depositing tungsten-containing materials into small and, especially,high aspect ratio features may cause formation of seams (e.g., unfilledvoids) inside the filled features. Large seams may lead to highresistance, contamination, loss of filled materials, and otherwisedegrade performance of integrated circuits. For example, a seam mayextend close to the field region after filling process and then openduring chemical-mechanical planarization.

SUMMARY

Methods and apparatuses for filling high aspect ratio features withtungsten-containing materials in a substantially void-free manner areprovided. In certain embodiments, the method involves depositing aninitial layer of a tungsten-containing material followed by selectivelyremoving a portion of the initial layer to form a remaining layer, whichis differentially passivated along the depth of the high-aspect rationfeature. In certain embodiments, the remaining layer is more passivatednear the feature opening than inside the feature. The method may proceedwith depositing an additional layer of the same or other material overthe remaining layer. The deposition rate during this later depositionoperation is slower near the feature opening than inside the featuresdue to the differential passivation of the remaining layer. Thisdeposition variation, in turn, may aid in preventing premature closingof the high-aspect ratio feature and facilitate filling of the featurein a substantially void free manner.

In certain embodiments, a method of filling a high aspect ratio feature,which is provided on a partially manufactured semiconductor substrate,involves introducing a tungsten-containing precursor and reducing agentinto a processing chamber and depositing a layer of atungsten-containing material on the substrate via a chemical vapordeposition reaction between the tungsten-containing precursor andreducing agent. The deposited layer at least partially fills thefeature. The method continues with introducing an activated etchingmaterial into the processing chamber and removing a portion of thedeposited layer using the activated etching material to form a remaininglayer. The method then proceeds with reintroducing thetungsten-containing precursor and reducing agent into the chamber andselectively depositing an additional layer of the tungsten-containingmaterial on the substrate, over the remaining layer, via a chemicalvapor deposition reaction between the precursor and reducing agent. Theadditional deposited layer is thicker inside the feature than near thefeature's opening. For purposes of this document, the term “inside thefeature” represent a middle portion of the feature located about themiddle point of the feature along the feature's depth, e.g., an areabetween about 25% and 75% or, more specifically, between about 40% and60% along the feature's depth measured from the feature's opening. Theterm “near the opening of the feature” or “near the feature's opening”represents a top portion of the feature located within 25% or, morespecifically, within 10% of the opening's edge or other elementrepresentative of the opening's edge.

In certain embodiments, the processing chamber is be maintained at apressure of less than 5 Torr while removing the portion of the depositedlayer. The processing chamber may be maintained at a pressure of lessthan 2 Torr during this operation. In certain embodiments, the remaininglayer is selectively or differentially passivated such that thispassivation is greater near the feature's opening than inside thefeature. For purposes of this document, a layer is said to be“passivated” when the layer inhibits deposition of additional materialsover the passivate layer's surface. A more passivated layer causes aslower deposition and/or delayed deposition than a similar but lesspassivated layer. In the same or other embodiments, the remaining layeris thinner near the feature's opening than inside the feature. Theremaining layer may have a thickness of less than 10% of the feature'sopening in some embodiments. More tungsten-containing material may beremoved near the feature's opening than inside the feature during theremoval operation. For example, a reduction in a thickness of thedeposited layer (to form the remaining layer) near the opening of thehigh aspect ratio feature may be at least about 25% greater than insidethe feature.

In certain embodiments, selectively depositing the additional layerinvolves filling, in a substantially void-free manner, at least a lowerhalf of the high aspect ratio feature. The high-aspect ratio feature hasan aspect ratio of at least about 2. In the same or other embodiments,removing the portion of the deposited layer is performed in a masstransport regime. An apparatus containing multiple processing chambersmay be used for filing the high-aspect ratio feature. In theseembodiments, depositing the layer of the tungsten-containing material,removing the portion of the deposited layer, and selectively depositingthe additional layer of the tungsten-containing material may beperformed in different processing chambers maintained at differentenvironmental conditions. In certain embodiments, the substrate has asecond feature that is closed during the deposition operation andremains closed after the removal operation. In the same or anotherembodiment, the high aspect ratio feature is closed during thedeposition operation and opens during the selective removal.

In certain embodiments, the method also involves applying photoresist tothe partially manufactured semiconductor substrate, exposing thephotoresist to light, and patterning the photoresist to create a patternand transferring the pattern to the partially manufactured semiconductorsubstrate.

Provided also is a method that involves introducing atungsten-containing precursor and a reducing agent into a processingchamber and depositing a layer of a tungsten-containing material on thepartially manufactured semiconductor substrate via a chemical vapordeposition reaction between the tungsten-containing precursor andreducing agent. The deposited layer partially fills the high aspectratio feature. The method continues with introducing an activatedetching material into the processing chamber and selectively removing aportion of the deposited layer to form a remaining layer of thetungsten-containing material. The remaining layer has various levels ofpassivation along the depth of the high aspect ratio feature and beingmore passivated near a feature opening than inside the feature. Thelevels of passivation of the remaining layer may depend on amounts ofthe tungsten-containing material removed from specific areas of thelayer to form the remaining layer. For example, more material may beremoved near the feature opening than inside the feature. In certainembodiments, the method also includes depositing additionaltungsten-containing material into the high aspect ratio feature, suchthat more material is deposited inside the feature than near the featureopening due to the remaining layer having various levels of passivationalong the depth of the feature.

Provided also is a method that involves providing the partiallymanufactured semiconductor substrate having a high aspect ratio featurethat is less than about 50 nanometers in size and has an aspect rationof at least about 4. The substrate may also include a protective layerdeposited at least within this feature. The method proceeds withintroducing a tungsten-containing precursor and a reducing agent intothe chamber and depositing a layer of a tungsten-containing material onthe substrate via a chemical vapor deposition reaction between thetungsten-containing precursor and reducing agent. The layer has athickness of less than about half the size of the feature to preventclosure of the feature. The method then continues with introducing anactivated etching material into the processing chamber and removing aportion of the deposited layer using the activated etching material at apressure of less than 5 Torr for a period of time determined by thethickness of the deposited layer. The method proceeds with introducingagain the tungsten-containing precursor and reducing agent into thechamber and selectively depositing an additional layer of thetungsten-containing material on the substrate, over the remaining layer,via the chemical vapor deposition reaction between thetungsten-containing precursor and the reducing agent. The deposition isperformed such that an interior deposition rate inside the feature is atleast twice higher than an exterior deposition rate near the featureopening. The selective deposition may be configured to fill at least abottom half of the feature. In certain specific embodiments, the highaspect ratio feature is about 30 nanometers in size and has a depth ofabout 250 nanometers. In these embodiments, the duration of the removaloperation may be between about 1 second and 10 seconds. In certainembodiments, the exterior deposition rate is less than about 100Angstroms per minute for at least first 30 seconds of the selectivedeposition.

Provided also is a semiconductor processing apparatus for filling a highaspect ratio feature on a partially manufactured semiconductorsubstrate. The apparatus may include a first processing chamber havingone or more deposition stations for positioning the substrate. The firstprocessing chamber is configured to deposit a layer of atungsten-containing material on the substrate via a chemical vapordeposition reaction. The one or more deposition stations may include adeposition heating element for controlling a temperature of thesubstrate during deposition. The apparatus also include a secondprocessing having one or more etching stations for positioning thesubstrate. The second processing chamber is configured to remove aportion of the deposited layer. The one or more etching stations mayinclude an etching heating element for controlling the temperature ofthe substrate during etching. Furthermore, the apparatus includes acontroller comprising program instructions for introducing thetungsten-containing precursor and the reducing agent into the firstprocessing chamber. In certain embodiments, additional instructionsinclude, after introducing the tungsten-containing precursor and thereducing agent into the first processing chamber, introducing anactivated etching material into the second processing chamber at apressure of less than 5 Ton for a period of between about 1 second and10 seconds. The instructions further include, after introducing anactivated etching material into the second processing chamber,introducing the tungsten-containing precursor and the reducing agentinto the first processing chamber or another processing chamber. Incertain embodiments, the apparatus also includes a wafer stepper.

Provided also is a non-transitory computer machine-readable mediumincluding program instructions for control of a semiconductor processingapparatus for filling a high aspect ratio feature provided on apartially manufactured semiconductor substrate. In certain embodiments,the program instructions include code for introducing thetungsten-containing precursor and the reducing agent into the firstprocessing chamber, code for introducing an activated etching materialinto the second processing chamber at a pressure of less than 5 Torr fora period of between about 1 second and 10 seconds, and code forintroducing the tungsten-containing precursor and the reducing agentinto the first processing chamber or another processing chamber.

These and other aspects of the invention are further described in moredetail with reference to the corresponding drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an example of a semiconductor substrate containing ahigh aspect ratio feature at different stages of a process in accordancewith certain embodiments.

FIG. 2 illustrates a general process flowchart representing a method offilling high aspect ratio features with tungsten-containing materials inaccordance with certain embodiments.

FIG. 3 illustrates schematic representations of substrate cross-sectionsat different stages of a filling process in accordance with certainembodiments.

FIG. 4 illustrates a schematic representation of an apparatus, inaccordance with certain embodiments, for filling high aspect ratiofeatures.

FIG. 5A shows a schematic illustration of a multi-station apparatus, inaccordance with certain embodiments, for filling high aspect ratiofeatures.

FIG. 5B is a schematic illustration of a multi-chamber apparatus, inaccordance with certain embodiments, for filling high aspect ratiofeatures.

FIG. 6A illustrates a schematic representation of a feature provided ina partially manufactured semiconductor substrate with atungsten-containing layer deposited in the feature and specifiesdifferent points of measurements of the layer thickness.

FIG. 6B illustrates a graph of the thickness distribution of thetungsten-containing layer shown in FIG. 6A before etching and afteretching for two different process conditions.

FIG. 7 is a plot of etching rates of activated fluorine species andrecombined fluorine species as a function of the pedestal temperature.

FIG. 8 is a plot of an etching rate of activated fluorine species as afunction of the chamber pressure.

FIG. 9 is a plot of deposition thicknesses as a function of time forvarious samples processed using different etching conditions.

FIG. 10 illustrates a cross-sectional Scanning Electron Microscopy (SEM)image of a 30-nanometer feature after initial tungsten deposition,3-second etch, and additional tungsten deposition.

FIG. 11 illustrates a cross-sectional SEM image of another 30-nanometerfeature after the same initial tungsten deposition, 1-second etch, andthe same additional tungsten deposition.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

In the following description, numerous specific details are set forth inorder to provide a thorough understanding of the present invention. Thepresent invention may be practiced without some or all of these specificdetails. In other instances, well known process operations have not beendescribed in detail to not unnecessarily obscure the present invention.While the invention will be described in conjunction with the specificembodiments, it will be understood that it is not intended to limit theinvention to the embodiments.

Introduction

Filling features with tungsten-containing materials may cause formationof seams inside the filled features. A seam can form when a layer thatis being deposited on the side walls of the feature thickens to thepoint that it seals off (i.e., forms a pinch point, also referred to asa sealing point) a void space below this point from the environment ofthe processing chamber. In the other words, thickening of the depositedlayer pinches off a void space. This pinching prevents precursors and/orother reactants from entering remaining void spaces, and they remainunfilled. A void space is typically an elongated seam extendingthroughout a portion of the filled feature along the feature's depthdirection. This void space or seam is also sometimes referred to as akeyhole because of its shape.

There are multiple potential causes for seam formation. One is anoverhang formed near the feature opening during deposition oftungsten-containing materials or, more typically, other materials, suchas a diffusion barrier layer or a nucleation layer. FIG. 1 illustratesan example of a semiconductor substrate containing a high aspect ratiofeature during different stages of semiconductor processing inaccordance with certain embodiments. The first cross-section 101 shows asubstrate 103 with a pre-formed feature hole 105. The substrate may be asilicon wafer, e.g., 200-mm wafer, 300-mm wafer, 450-mm wafer. Thefeature hole 105 may have an aspect ratio of at least about 2:1 or, inmore specific embodiments, of at least about 4:1. The features hole 105may also have a cross-section dimension near the opening (e.g., openingdiameter, line width, etc.) of between about 10 nanometers to 500nanometers, or more specifically between about 25 nanometers to 300nanometers. The feature hole is sometimes referred to as an unfilledfeature or simply a feature.

In the next stage (cross-section 111), the substrate 103 is shown with adeposited an under-layer 113 lining the feature hole 105, which may be adiffusion barrier layer, an adhesion layer, a nucleation layer, acombination of thereof, or any other applicable material. Because manydeposition processes do not have good step coverage properties, i.e.,more material is deposited on the field region and near the opening thaninside the feature, the under-layer 113 may form an overhang 115. Whilethe overhang 115 is a part of the under-layer 113, the layer 113 may bethicker near the opening than, for example, inside the feature. For thepurposes of this description, “near the opening” is defined as anapproximate position or an area within the feature (i.e., along the sidewall of the feature) corresponding to between about 0-10% of the featuredepth measured from the field region. In certain embodiments, the areanear the opening corresponds to the area at the opening. Further,“inside the feature” is defined as an approximate position or an areawithin the feature corresponding to between about 20-60% of the featuredepth measured from the field region on the top of the feature.Typically, when values for certain parameters (e.g., thicknesses) arespecified “near the opening” or “inside the feature”, these valuesrepresent a measurement or an average of multiple measurements takenwithin these positions/areas. In certain embodiments, an averagethickness of the under-layer near the opening is at least about 10%greater than that inside the feature. In more specific embodiments, thisdifference may be at least about 25%, at least about 50%, or at leastabout 100%. Distribution of a material within a feature may also becharacterized by its step coverage. For the purposes of thisdescription, “step coverage” is defined as a ratio of two thicknesses,i.e., the thickness of the material inside the feature divided by thethickness of the material near the opening. In certain examples, thestep coverage of the under-layer is less than about 100% or, morespecifically, less than about 75% or even less than about 50%.

The next cross-section 121 illustrates the feature hole filled with thetungsten-containing materials 123. A deposition process may result in aconformal layer of the materials 123 built-up over the under-layer 113.This deposited layer follows the shape of the under-layer 113 includingits overhang 115. In certain embodiments and, particularly, in laterstages of the deposition process (e.g., right before feature closing),the layer 123 may become less conformal resulting in poor step coverage(i.e., more material being deposited near the opening than inside thefeature). As the layer 123 thickens, it may close the feature forming apinch point 125. Often some additional material is deposited above thepinch point 125 before the deposition process is stopped. Because of theoverhang 115 and, in certain embodiments, the poor step coverage of thelayer 123, the closed feature may have an unfilled void 129 (i.e., aseam) below the reference point 125. The size of the void 129 and theposition of the reference point 125 with respect to the field region 127depend on the size of the overhang 115, as well as the size, aspectratio, and bowing of the feature, deposition process parameters, andother parameters.

Finally, cross-section 131 shows the substrate 133 afterchemical-mechanical planarization (CMP), which removes a top layer fromthe substrate 103. CMP may be used to remove an overburden from thefield region, such as parts of layers 113 and 123 that were present onthe top surface of the substrate 103. Typically the substrate 103 isalso thinned down during CMP to form the substrate 133. If the pinchpoint 125 falls above the planarization level of the CMP process, as inFIG. 1, the seam 129 opens up and is exposed to environment through theseam opening 135. The problems with open and large seams are describedabove.

Another cause that is not illustrated in FIG. 1 but that neverthelessmay lead to seam formation or enlarging seams and moving the referencepoint closer to the field region is curved (or bowed) side walls offeature holes, which are also referred to as bowed features. In a bowedfeature the cross-sectional dimension of the cavity near the opening issmaller than that inside the feature. Effects of these narrower openingsin the bowed features are somewhat similar to the overhang problemdescribed above. Further, bowed features may also have under-layers withoverhangs and encounter other seam formation causes compounding negativeeffects of seam formation.

Complete eliminations of seams from the features filled withtungsten-containing materials may not be possible or practical. Somevoid spacing may remain inside the features, for example, due to largegrains of the deposited materials, mass transport limitations duringdeposition, especially before feature closing, and other reasons.However, novel methods are presented herein that allow reducing seamsizes and moving reference points further away from the field region.These are collectively referred to as mitigating seam formation.

Process

It has been found that seam formation can be mitigated or, in someembodiments, eliminated by introducing one or more intermediateselective removal operations. For example, a filling process may startwith forming an initial layer that at least partially fills a highaspect ratio feature. This operation is followed by partial selectiveremoval of this initial layer and then depositing an additional layer.This removal-deposition cycle may be repeated until the feature iscompletely filled in a substantially void free manner. Processparameters may be selected such that the step coverage is improved atleast one cycle. In certain embodiments, each cycle further improves thestep coverage. Overall, selective removal can be characterized by morematerial removed near the opening than inside the feature. Variousprocess control parameters may be employed to achieve these resultsincluding removal at mass-transport limiting conditions, controllingremoval and/or adsorption rates of different etching components (e.g.,activated and recombined species), controlling recombination rates ofetching species, and others. For the purposes of this application,activated species, such as atomized species, radicals, and ions (e.g.,atomic fluorine), are distinguished from recombined species, such asmolecules including high energy state molecules (e.g., molecularfluorine), and from initial etchant species (e.g., nitrogen tri-fluorideand other precursors further described below).

FIG. 2 illustrates a general process flowchart representing a method offilling high aspect ratio features with tungsten-containing materials inaccordance with certain embodiments. A process 200 may start withpositioning a substrate containing high aspect ratio features on adeposition station inside the processing chamber (block 201). Thesubstrate may also have an under-layer, such as a diffusion barrierlayer and/or tungsten nucleation layer. Certain substrate andunder-layer details are provided above in the context of FIG. 1. Incertain embodiments, an average thickness of an under-layer near thefeature opening is at least about 25% greater than that inside thefeature (e.g., near the bottom of the feature). In a more general sense,a substrate may have an under-layer that formed overhangs. In somecases, a layer of previously deposited bulk tungsten may be present inthe feature. Features with overhangs are more prone to form voids duringfilling.

A diffusion barrier layer may be previously deposited onto the substrateto form a conformal layer that prevents diffusion of materials used tofill the features into surrounding materials of the substrate. Materialsfor the diffusion barrier layer may include tungsten nitride, titanium,titanium nitride, and others. The barrier layer may be between about 10Angstroms and 500 Angstroms thick or, in more specific embodiments,between about 25 Angstroms and 200 Angstroms thick. In certainembodiments, a diffusion barrier layer is unevenly distributed on thesubstrate surface such that it forms overhang.

A nucleation layer is typically a thin conformal layer that facilitatessubsequent deposition of bulk tungsten-containing material thereon. Incertain embodiments, the nucleation layer is deposited using a pulsednucleation layer (PNL) technique. In a PNL technique, pulses of thereducing agent, purge gases, and tungsten-containing precursor aresequentially injected into and purged from the reaction chamber. Theprocess is repeated in a cyclical fashion until the desired thickness isachieved. PNL broadly embodies any cyclical process of sequentiallyadding reactants for reaction on a semiconductor substrate, includingatomic layer deposition (ALD) techniques. PNL techniques for depositingtungsten nucleation layers are described in U.S. patent application Ser.No. 12/030,645 filed on Feb. 13, 2008, U.S. patent application Ser. No.11/951,236, filed Dec. 5, 2007, and U.S. patent application Ser. Nos.12/407,541, filed on Mar. 19, 2009, all of which are incorporated byreference herein its entirety for the purposes of describing tungstendeposition process. Additional discussion regarding PNL type processescan be found in U.S. Pat. Nos. 6,635,965, 6,844,258, 7,005,372 and7,141,494 as well as in U.S. patent application Ser. No. 11/265,531,also incorporated herein by reference. In certain embodiments, anucleation layer is unevenly distributed on the substrate surface suchthat it forms overhang. The methods described herein are not limited toa particular method of tungsten nucleation layer deposition, but includedeposition of bulk tungsten film on tungsten nucleation layers formed byany method including PNL, ALD, CVD, PVD and any other method. Moreover,in certain embodiments, bulk tungsten may be deposited directly withoutuse of a nucleation layer.

The deposition station may be also used to perform certain prioroperations (e.g., deposition of a diffusion barrier layer, deposition ofa nucleation layer) and/or subsequent operations (e.g., etching, anotherdeposition, final feature filling). In certain embodiments, thedeposition station may be specifically designated to perform depositionoperation 203. The apparatus may also include additional depositionstations to perform the operation 203. For example, an initialdeposition may be performed on the first deposition station. Thesubstrate may be then moved to another station for etching. In certainembodiments further described below, an etching station is positioned ina different chamber to prevent cross-contamination between depositionand etching environments that use different materials and conditions fortheir respective operations. If the process then requires anotherdeposition operation 203, the substrate may be returned back to thefirst deposition station or moved to another deposition station.Multiple deposition stations may be also used to perform paralleldeposition operation 203 on several substrates. Additional details andapparatus embodiments are explained below in the context of FIG. 4 andFIGS. 5A-B.

The process may proceed with deposition of tungsten-containing materialsonto the substrate (block 203). In certain embodiments, bulk depositioninvolves a chemical vapor deposition (CVD) process in which atungsten-containing precursor is reduced by hydrogen to deposittungsten. While tungsten hexafluoride (WF₆) is often used, the processmay be performed with other tungsten precursors, including, but notlimited to, tungsten hexachloride (WCl₆), organo-metallic precursors,and precursors that are free of fluorine such as MDNOW(methylcyclopentadienyl-dicarbonyInitrosyl-tungsten) and EDNOW(ethylcyclopentadienyl-dicarbonyInitrosyl-tungsten). In addition, whilehydrogen is generally used as the reducing agent in the CVD depositionof the bulk tungsten layer, other reducing agents including silane maybe used in addition or instead of hydrogen without departing from thescope of the invention. In another embodiment, tungsten hexacarbonyl(W(CO)₆) may be used with or without a reducing agent. Unlike with thePNL processes described above, in a CVD technique, the WF₆ and H₂ orother reactants are simultaneously introduced into the reaction chamber.This produces a continuous chemical reaction of mix reactant gases thatcontinuously forms tungsten film on the substrate surface. Methods ofdepositing tungsten films using chemical vapor deposition (CVD) aredescribed in U.S. patent application Ser. No. 12/202,126 filed Aug. 29,2008, which is incorporated herein its entirety for the purposes ofdescribing deposition processes. According to various embodiments, themethods described herein are not limited to a particular method ofpartially filling a feature but may include any appropriate depositiontechnique.

FIG. 3 illustrates schematic representations of one example of thefeatures' cross-sections at different stages of a filling process.Specifically, cross-section 321 represents an example of the featureafter completing one of the initial deposition operations 203. At thisstage of the process, substrate 303 may have a layer 323 oftungsten-containing materials deposited over under-layer 313. The sizeof the cavity near the opening may be narrower that inside the feature,for example, due to overhang 315 of the under-layer 313 and/or poor stepcoverage of the deposited layer 323, which are described in more detailabove in the context of FIG. 1.

Returning to FIG. 2, the deposition operation 203 proceeds until thedeposited layer (e.g., the layer 323) reaches a certain thickness. Thisthickness may depend on the cavity profile and opening size. In certainembodiments, the average thickness of the deposited layer near theopening may be between about 5% and 25% of the feature cross-sectionaldimension including any under-layers, if ones are present. In otherembodiments, the feature may be completely closed during the depositionoperation 203 and then later re-opened during the selective removaloperation (not shown).

In certain embodiments, a process chamber may be equipped with varioussensors to perform in-situ metrology measurements to identify the extentof the deposition operation 203 and the removal operation 205. Examplesof in-situ metrology include optical microscopy and X-Ray Fluorescence(XRF) for determining thickness of deposited films. Further, infrared(IR) spectroscopy may be used to detect amounts of tungsten fluorides(WFx) generated during etching operation. Finally, an under-layer, suchas tungsten nucleation layer or a diffusion barrier layer, may be usedas an etch-stop layer.

The process continues with a selective removal operation 205. Certaindetails of etching processes are described in U.S. patent applicationSer. No. 12/535,377, entitled “METHOD FOR DEPOSITING TUNGSTEN FILMHAVING LOW RESISTIVITY, LOW ROUGHNESS AND HIGH REFLECTIVITY” byChandrashekar et al., filed Aug. 4, 2009, which is incorporated hereinin its entirety. The substrate may be moved from the deposition stationto another station and, in more specific embodiment, another processingchamber with operating at different conditions, may continue beingprocessed on the same station, or may be first removed from thedeposition station (e.g., for storage) and then returned back to thedeposition station for the selective removal of the deposited layer.

One way to achieve selective removal (i.e., to remove more depositedmaterial near the opening than inside the feature) is to performoperation 205 in a mass transport limited regime. In this regime, theremoval rate inside the feature is limited by amounts of and/or relativecompositions of different etching material components (e.g., an initialetchant material, activated etchant species, and recombined etchantspecies) that diffuse into the feature. In certain examples, etchingrates depend on various etchant components' concentrations at differentlocations inside the feature. It should be noted that the terms“etching” and “removal” are used interchangeably in this document. Itshould be understood that selective removal could be performed using anyremoval techniques, which includes etching as well as other techniques.

Mass transport limiting conditions may be characterized, in part, byoverall etchant concentration variations. In certain embodiments, thisconcentration is less inside the feature than near its opening resultingin a higher etching rate near the opening than inside. This in turnleads to selective removal. Mass transport limiting process conditionsmay be achieved by supplying limited amounts of etchant into theprocessing chamber (e.g., use low etchant flow rates relative to thecavity profile and dimensions), while maintaining relative high etchingrates in order to consume some etchant as it diffuses into the feature.In certain embodiment, a concentration gradient is substantial, whichmay be caused relatively high etching kinetics and relative low etchantsupply. In certain embodiments, an etching rate near the opening mayalso be mass limited, but this condition is not required to achieveselective removal.

In addition to the overall etchant concentration variations inside highaspect ratio features, selective removal may be influenced by relativeconcentrations of different etchant components throughout the feature.These relative concentrations in turn depend by relative dynamics ofdissociation and recombination processes of the etching species. Asfurther described below, an initial etchant material is typically passedthrough a remote plasma generator and/or subjected to an in-situ plasmain order to generate activated etchant species (e.g., fluorine atoms,radicals). However, activated specifies tend to recombine into lessactive recombined etching species (e.g., fluorine molecules) and/orreact with tungsten-containing materials along their diffusion paths. Assuch, different parts of the deposited tungsten-containing layer may beexposed to different concentrations of different etchant materials,e.g., an initial etchant, activated etchant species, and recombinedetchant species. This provides additional opportunities for controllingselective removal as described below.

For example, activated fluorine species are generally more reactive withtungsten-containing materials than initial etching materials andrecombined etching materials. Furthermore, as evident from FIG. 7, theactivated fluorine species are generally less sensitive to temperaturevariations than the recombined fluorine species. Therefore, processconditions may be controlled in such a way that removal is predominantlyattributed to activated fluorine species. Furthermore, specific processconditions may result in activated fluorine species being present athigher concentrations near features' openings than inside the features.For example, some activated species may be consumed (e.g., react withdeposited materials and/or adsorbed on its surface) and/or recombinedwhile diffusing deeper into the features, especially in small highaspect ratio features. It should be noted that recombination ofactivated species also occurs outside of high aspect ratio features,e.g., in the showerhead of the processing chamber, and depends on achamber pressure. Therefore, a chamber pressure may be specificallycontrolled to adjust concentrations of activated etching species atvarious points of the chamber and features. These and other processconditions will now be described in more detail.

In certain embodiments, selective removal operation 205 involvesintroducing an initial etchant material into the processing chamber andusing it to selectively remove the deposited layer. An etchant selectiondepends on a deposited material. While this description focuses ontungsten containing materials, such as tungsten and tungsten nitride, itshould be understood that other materials may be used for partial orcomplete filling of high aspect ratio features. Some example of thesematerials include such as titanium, titanium nitride, tantalum, tantalumnitride, ruthenium, and cobalt. These materials can be deposited usingPhysical Vapor Deposition (PVD), Chemical Vapor Deposition (CVD), AtomicLayer Deposition (ALD), and other deposition techniques. In general,operation 205 may be used to selectively remove any materials formedinside high aspect ratio features, including diffusion barrier layers,nucleation layers, and/or filling materials.

Example of initial etchant materials that can be used for selectiveremoval of tungsten containing materials and some other materialsinclude nitrogen tri-fluoride (NF₃), tetra-fluoro-methane (CF₄),tetrafluoroethylene (C₂F₄), hexafluoroethane (C₂F₆), andoctafluoropropane (C₃F₈), tri-fluoro-methane (CHF₃), sulfur hexafluoride(SF₆), and molecular fluorine (F₂). A process typically involvesgenerating activate species, e.g., including radicals, ions, and/or highenergy molecules. For example, an initial material may be flown througha remote plasma generator and/or subjected to an in-situ plasma.

Flow rates of the etchant typically depend on a size of the chamber,etching rates, etching uniformity, and other parameters. Typically, aflow rate is selected in such a way that more tungsten-containingmaterial is removed near the opening than inside the feature. In certainembodiments, these flow rates cause mass-transport limited selectiveremoval. For example, a flow rate for a 195-liter chamber per stationmay be between about 25 sccm and 10,000 sccm or, in more specificembodiments, between about 50 sccm and 1,000 sccm. In certainembodiments, the flow rate is less than about 2,000 sccm, less thanabout 1,000 sccm, or more specifically less than about 500 sccm. Itshould be noted that these values are presented for one individualstation configured for processing a 300-mm wafer substrate. A personhaving ordinary skills in the art would understand that, for example,these flow rates can be scaled up or down depending on a substrate size,a number of stations in the apparatus (e.g., quadruple for a fourstation apparatus), a processing chamber volume, and other factors.

In certain embodiments, the substrate needs to be heated up or cooleddown before the removal operation 205 can proceed. Various devices maybe used to bring the substrate to the predetermined temperature, such asa heating or cooling element in a station (e.g., an electricalresistance heater in stalled in a pedestal or a heat transfer fluidcirculated through a pedestal), infrared lamps above the substrate,igniting plasma, etc.

A predetermined temperature for the substrate is selected in such a wayto not only induce a chemical reaction between the deposited layer andvarious etchant species but also to control the rate of the reactionbetween the two. For example, a temperature may be selected to have highremoval rates such that more material is removed near the opening thaninside the feature. Furthermore, a temperature may be also selected tocontrol recombination of activated species (e.g., recombination ofatomic fluorine into molecular fluorine) and/or control which species(e.g., activated or recombined species) contribute predominantly toetching. Overall, the substrate temperature may be selected based onetchant chemical compositions, a desired etching rate, desiredconcentration distributions of activated species, desired contributionsto selective removal by different species, and other material andprocess parameters. In certain embodiments, a substrate is maintained atless than about 300° C., or more particularly at less than about 250°C., or less than about 150° C., or even less than about 100° C. In otherembodiments, a substrate is heated to between about 300° C. and 450° C.or, in more specific embodiments, to between about 350° C. and 400° C.Other temperature ranges may be used for different types of etchants.

It has been determined that activated species provide not only fasterbut also more desirable selective removal than their recombinedcounterparts. As such, various approaches have been developed toincrease relative concentrations and/or removal contributions of theactivated species. For example, activation energy of activated fluorinespecies is much less than that of the recombined fluorine. Therefore,lowering substrate temperatures may result in more removal contributionfrom activated species. At certain temperatures (and other processconditions, e.g., flow rates and chamber pressures), a relative removalcontribution of the activated species may exceed that of the recombinedspecies.

FIG. 7 is a plot of two etching rates as a function of the pedestaltemperature for activated species (line 702) and for recombined species(line 704). Etching tests were modeled using a nitrogen tri-fluorideprecursor supplied into the processing chamber through a remote plasmagenerator at 400 sccm for 20 seconds (line 702) and a molecular fluorineprecursor supplied at 500 sccm for 50 seconds (line 704). The chamberpressure was kept at 1 Torr during both tests. The results indicate thatthe etch rate corresponding to the recombined fluorine molecules (line704) can be substantially reduced by lowering the pedestal temperature.At the same time, the etch rate corresponding to the activated species(line 702) remains relative flat, i.e., it is not as sensitive to thepedestal temperature as line 702.

In certain embodiments, it may be difficult to eliminate or evensubstantially minimize recombined species from contacting the substratesurface (e.g., to minimize recombination of activated species). Forexample, an apparatus typically include a showerhead (further explainedin the context of FIG. 4), which causes substantial recombination ofpreviously activated etchant species (e.g., flowing from a remote plasmagenerator through a showerhead). This may be a result, for example, of alonger residence time within a closed volume of the showerhead and itshigh surface-to-volume ratio. While recombination may be still presentin the system, it has been determined that effect of recombined speciesof partial removal may be reduced by a substrate temperature during thisoperation. Atomic fluorine has much lower activation energy thanmolecular fluorine (0.33 eV v. 0.55 eV). This relationship generallyholds for other activated and recombined species. As such, etchingcontributions of recombined species can be reduced by loweringtemperature during the etching operation.

Another process parameter that may effect recombination of activatedspecies is a pressure inside the chamber or, more specifically, partialpressures of different materials that may be present in the chamber(e.g., initial etchant materials, activated species, recombined species,carrier gases, reaction products, etc.). A higher total pressure (e.g.,greater than about 10 Torr) generally corresponds to shorter mean freepaths of the activated etchant species resulting in more collisionsbetween the species, which in turn results in a higher recombinationrate. Furthermore, it has been found that a sticking probability of somerecombined species (e.g., molecular fluorine) on a tungsten surface orother similar surfaces is lower than that of activated species (e.g.,atomic fluorine) at low pressure levels. A low sticking probabilitytends to improve step coverage.

FIG. 8 is a plot of an etch rate as a function of the chamber pressurefor a nitrogen tri-fluoride precursor supplied into the processingchamber at 400 sccm for 20 seconds. The substrate was kept at 300° C.during this experiment. The results show that between 1 Torr and 5 Torran increase in pressure resulted in lower etching rates. Without beingrestricted to any particular theory, it is believed that higherpressures at this level leads to higher recombination rates of activatedspecies into recombined species, which are less reactive leading tolower etching rates. This recombination and lower etching reactivityactually offsets any increases caused by higher overall etchantconcentrations. As pressure further increased above 5 Torr, higherconcentrations of etching materials results in some moderate increasesin etching rates. It is believed that removal is predominantlycontrolled by the recombined species at this pressure levels. As such inorder to have a greater contribution from activated species, a processchamber needs to be kept at lower overall pressure values. In certainembodiments, a process chamber is maintained at less than about 5 Torr,or more specifically at less than about 2 Torr, or even at less thanabout 1 Torr or less than about 0.1 Torr.

Returning to FIG. 2, the reduction in the average thickness of thedeposited layer near the opening may be greater than that inside thefeature as a result of the selective removal operation 205. In certainembodiments, the reduction near the opening is at least about 10%greater than the reduction inside the feature or, in more specificembodiments, is at least about 25% greater. The removal operation 205may generally be performed up to the point at which the substrate or anyunder-layer, if one is present, is exposed to the etchant. The remaininglayer may be characterized with step coverage. In certain embodiments,step coverage of the etched layer is at least about 75%, morespecifically at least about 100%, or at least about 125%, more even morespecifically at least about 150%.

In certain embodiments, a removal operation is performed such that apassivated surface is formed. This surface inhibits deposition oftungsten-containing materials in the subsequent deposition cycle.Forming a passivated surface is described below in the context of FIG.2, though it should be noted that it is not so limited and may beperformed in any tungsten deposition process by appropriately employingan etch process. Passivation, and thus subsequent tungsten deposition,may be selective or non-selective with respect to the feature depth orother geographic region of deposition surface, by appropriately tuningthe etching conditions as described herein.

Returning to FIG. 2, in certain embodiments, the selective removaloperation 205 is performed at certain process conditions that result information of a layer, which may be referred to as a remaining layer,having a passivated surface. In certain embodiments, the passivation isdifferential along the depth of the high aspect ratio features due todifferent etching conditions (e.g., concentrations of activated species)along this dimension as described above. For example, process conditionsduring this operation may be specifically tuned to cause morepassivation near the features' openings than inside the features.Generally, these conditions correspond to low pressures (e.g., less than8 Torr and even less than 5 Torr) and prolonged etching (e.g., more than1 seconds and even more than 5 seconds for typical 30-nanometerfeatures). This phenomenon will now be described in more detail withreference to FIG. 9.

FIG. 9 is a plot of second deposition cycle deposition thicknesses as afunction of time for five sets of wafers processed using differentetching conditions. This plot illustrates effects of differentpassivation levels caused by these etching conditions on depositionrates. In this experiment, surfaces of the five sets of wafers weredeposited with an initial tungsten layer. The same deposition conditionswere used for all five sets. Then each set of wafers was processed usingdifferent etching conditions. The first set of wafers corresponding toline 902 in FIG. 9 (the top solid identified by numerical values 133,354, and 545 in the plot) was not etched at all. In other words, thefirst deposition cycle was followed by the second deposition cyclewithout any intermediate etching cycles. The second set of waferscorresponding to line 904 (the middle dashed line identified by anumerical value 526; other numerical values not shown because of theclose proximity to the other two lines) was etched at 18 Torr for aperiod of 7 seconds. The third set of wafers corresponding to line 906(the bottom solid line in the top group of three lines identified bynumerical values 126, 344, and 517) was etched at 18 Torr for a periodof 17 seconds. The fourth set of wafers corresponding to line 908(identified by numerical values 54, 99, and 149) was etched at 0.8 Torrfor a period of 5 seconds. Finally, the fifth set of waferscorresponding to line 908 (identified by numerical values 5, 9, and 25)was etched at 0.8 Torr for a period of 10 seconds. These five sets ofwafers were then subjected to same deposition conditions for threeperiods of time (i.e., 5 seconds, 15 seconds, and 25 seconds) to formaddition tungsten layers. The resulting thicknesses of these additionaltungsten layers are presented in FIG. 9.

FIG. 9 illustrates that the first three sets of wafers (i.e., the waferssubjected to no etching or etching at 18 Torr) have much thickeradditional tungsten layers deposited in the second deposition cycle thanthe last two sets of wafers (i.e., the wafers subjected to etching at0.8 Torr). As explained above with reference to FIG. 8, higher pressurelevels may result in recombination of activated etching species (e.g.,atomic fluorine into molecular fluorine) and, to a certain degree,different chemical reactions during etching. Resulting etched layersprocessed at different pressure levels during etching may have differentcharacteristics, such as chemical compositions and/or physicalstructures, at least on their exposed surfaces. This, in turn, impactsdeposition of the later deposited layers of tungsten as shown in FIG. 9.Specifically, FIG. 9 demonstrates that etching at a lower pressure andfor a longer period of time results in a more passivated remaining layerthat inhibits deposition of at least the subsequent layer. At the sametime, lower pressure levels correspond to more aggressive etching asevidenced from FIG. 8. A combination of pressure and etching durationshould be carefully controlled to prevent complete removal of theinitial deposited layer and deteriorating the underlying diffusionbarrier layer.

While some passivation is generally desirable near the feature'sopening, it is less desirable and, in certain embodiments, should beavoided inside the feature. It has been found that at certain processconditions high aspect ratio features become differentially passivatedduring etching such that the remaining layer is more passivated near theopening than inside the feature. Without being restricted to anyparticular theory, it is believed that etching at lower pressure levelsmay result in mass-transport limiting conditions within high aspectratio features where higher concentrations of the activated etchantspecies are present near the features' openings than inside thefeatures. Some activated etchant species are consumed during etching thelayer near the opening while some other activated species are recombinedwhile diffusing into the features.

Even passivation near the features' openings should be carefullycontrolled to prevent excessive passivation in these areas and allow forsufficient deposition during later operations in order to completelyfill and close the feature. This concern is reflected in FIGS. 10 and11. Specifically, FIG. 10 shows a cross-sectional Scanning ElectronMicroscopy (SEM) image of a 30-nanometer feature after initial tungstendeposition followed by 3-second etching and then additional tungstendeposition. The top area of this feature remained unfilled even thoughtthe bottom area is completely filled. While a gradual bottom-up fillcaused by differential passivation is desirable to avoid prematureclosing of the feature and formation of the seam, excessive passivationmay result in unfilled features such as the one presented in FIG. 10,which may not be desirable or acceptable. FIG. 11 shows across-sectional SEM image of another 30-nanometer feature after the sameinitial tungsten deposition followed by 1-second etching and then thesame additional tungsten deposition. The top portion of this feature wascompletely filled. In some cases, while some passivation near thefeatures' opening is desirable, over-passivation is avoided.

In light of these considerations, process conditions may be specificallytuned to achieve desirable processing results, such as completelyfilling high aspect ratio features in a substantially void free manner.Some of these process conditions include performing the removaloperation at a pressure of less than 5 Torr, or less than 2 Torr, oreven less than 1 Torr. In certain embodiments, the pressure ismaintained at between about 0.1 Ton and 5 Torr or, more specifically,between about 0.5 Torr and 3 Torr. Duration of the etching operationgenerally depends on a thickness of the initial layer, which, in turn,is generally kept to less than about a half of the feature size in orderto prevent closing of the feature. For example, an initial layerdeposited over the substrate surface containing 30-nanometer features isgenerally less than 15 nanometers. Such a layer may be etched for atleast about 1 second or, more specifically, for at least about 3seconds, or even at least about 5 seconds without damaging any of theunderlying layers. In specific embodiments, duration of the etchingoperation is between about 1 and 10 seconds or, even more specifically,between about 3 and 5 seconds. Etching conditions may be also describedwith reference to the remaining layer and the size of the feature. Incertain embodiments, the remaining layer has a thickness of less than10% of the feature opening.

In certain embodiments, the substrate may include one or more featuresthat are closed during the deposition operation 203 and remain closedduring the selective removal operation 205. For example, a substrate mayinclude small, medium size, and large features. Some small features mayclose during the initial deposition operation and never open again.Medium size features may close during later cycles and remain closedwhile other larger features are being filled. In certain embodiments,features may be present at different vertical levels of the substrates,e.g., in a dual-damascene arrangements. The features on lower-levels mayclose earlier than features in higher-levels.

In certain embodiments, the deposition operation 203 may onlytemporarily close the feature. Unlike closing the feature during a finalfilling operation, such as operation 213 described below, or in thesituation with multiple features of different sizes and verticalpositions described above, the seam during this temporary closure may bestill unacceptably large or start too close to the field region. Inthese embodiments, the selective removal operation 205 may be designedin such a way that the first part of the operation 205 is used tore-open the feature and then the next part of the operation 205 is usedfor selective removal of the deposited material. The process conditionsin these two parts may be the same or different. For example, theetchant flow rate may be higher during the first part of the operation205 and then decreased as the feature opens up.

A deposition-removal cycle including the deposition operation 203 andthe selective removal operation 205 may be repeated one or more times asindicated by decision block 207. For example, it may be difficult toachieve desirable step coverage after one cycle, particularly, in smallfeatures with large overhangs. Considerations in a decision 207 whetherto proceed with another cycle include overhang size, feature size,feature aspect ratio, feature bowing, as well as seam size and seamlocation requirements.

In certain embodiments, process parameters for one or both operations inthe next cycle may be changed (block 209). For example, net depositionduring initial cycles may need to be greater than in the later cyclesbecause the deposited layer is still thin layer and the risk ofcontamination during etching is high. At the same time, the cavity ismore open initially and the risk of closing is lower. For example,initial deposition cycles may be performed at slower deposition rates(e.g., driven by lower temperatures and/or chamber pressure) to achievegreater control over amounts of the tungsten containing materialsdeposited on the partially manufactured substrate. Slower rates may leadto a more conformal deposition as described above, which may be neededfor certain feature types, in particular small, high aspect ratiofeatures. Subsequent deposition cycles may be performed at fasterdeposition rates (e.g., driven by higher temperatures and/or chamberpressure) since control over a deposited thickness may be less criticaland/or previous deposition-etching cycles may have already modifiedprofiles of the cavities in such way that these cavities are less likelyto close prematurely. In other embodiments, deposition operation inlater cycles may be performed at slower deposition rated becauseremaining cavities are smaller and may be prone to premature closing.Likewise, etching process conditions may modified from one cycle toanother starting, for example, with less aggressive etching conditionswhile deposited layers are still thin and eventually turning to moreaggressive etching conditions.

Returning to FIG. 3, cross-section 331 depicts the feature afterselective removal. Thus, cross-sections 321 and 331 may represent thefirst cycle or, more generally, one of the initial cycles. The depositedlayer 323 during this cycle may be too thin to completely compensate foror offset various seam formation causes, such as the overhang 315. Forexample, after the selective removal operation the cavity shown incross-section 331 is still narrower near the opening than inside thefeature. In certain embodiments, this difference (how much narrower) maybe sufficiently small that the process continues to a final fillingoperation without repeating the deposition-removal cycle.

Cross-sections 341 and 351 illustrate the substrate 303 during and afterlater cycles. First, cross-section 341 shows a new deposited layer 343formed over etched layer 333. The feature with layer 343 may have animproved profile reflecting better step coverage achieved during theprevious cycles. However, the profile of the cavity may still not allowproceeding to final filling and another etching operation may be neededto further shape this cavity. Cross-section 351 represents the substrate303 at a stage prior to a final deposition to complete the fill. Thecavity is wider near the opening than inside the cavity. In certainembodiments, step coverage of the new deposited layer is at least about10% greater than that of the initially deposited layer or, in morespecific embodiments, at least about 20% greater or at least about 30%greater.

Returning to FIG. 2, in certain embodiments, the deposition operation203 and the selective removal operation 205 may be performedsimultaneously, which is represented by a block 204. For example, aprecursor and an etchant may be flown into the processing chamber at thesame time allowing for both deposition and etching reactions to occursimultaneously. In order to achieve greater net deposition inside thefeature than near the opening, at least initially, the flow rates of theetchant and the tungsten-containing precursor may be such that theetching reaction is mass-transport limited and, therefore, depends onthe etchant concentration. At the same time, the deposition reaction isnot mass-transport limited and proceeds at about the same rates insidethe feature and the opening. An etchant or precursor flow rate or bothmay be adjusted (e.g., gradually or in stepwise fashion) during theoperation 204, and at some point the etchant flow into the processingcamber may be discontinued. At this point, the process may transition toa final fill operation 213 described below.

After one or more deposition-removal cycles are performed to partiallyfill the feature and shape the feature profile, the process may thencontinue with a final filling operation 213. This operation may be insome aspects similar to the deposition operation 203. The maindistinction is that the operation 213 proceeds until the feature iscompletely closed and it is not followed by an etching operation to openthe feature. Returning to FIG. 3, cross-section 361 represents anexample of substrate 303 after the final filling operation. In certainembodiments, the feature still has a seam 363, but it is smaller and hasa reference point positioned further away from the field region than ina conventionally filled feature, such as the one illustrated in FIG. 1.In certain embodiments, the seam 363 ends at least about 20% from thefield region relative to the depth of the feature (i.e., a ratio ofD_(REF) to D_(FET) is at least about 20%).

In another embodiment, features are filled by depositing more tungsteninside the features than near the opening. Differential deposition ratesmay be achieved by inhibiting a surface onto which tungsten-containingmaterials are being deposited to different levels depending on theposition within the feature (e.g., near the opening or inside thefeature). Specifically, the surface near the opening may be inhibitedmore than the surface inside the feature. In a particular embodiment, aninhibitor is introduced into the processing chamber before a depositionoperation. The exposed surface of the feature is treated with thisinhibitor in a mass-transport limited regime similar to the onedescribed above in the context of etching. However, unlike the etchingoperation no material is removed from the surface (i.e., no net etch)during inhibiting. For example, at certain process conditionsfluorine-based etching of the deposited layer may lead to formation ofresidues (e.g., containing certain tungsten fluorides) on the surface ofthe remaining etched layer. These residues may act as an inhibitor in asubsequent deposition operation. Further, at certain process conditionsno net removal of materials from the deposited layer may occur, but thedeposited layer forms an inhibiting layer that is more prevalent nearthe opening than inside the feature. Filling the feature usingdifferential deposition rates as may be done in conjunction with or inlieu of the deposition-removal operations described above.

Apparatus

Any suitable chamber may be used to implement this novel method.Examples of deposition apparatuses include various systems, e.g., ALTUSand ALTUS Max, available from Novellus Systems, Inc. of San Jose,Calif., or any of a variety of other commercially available processingsystems.

FIG. 4 illustrates a schematic representation of an apparatus 400 forprocessing a partially fabricated semiconductor substrate in accordancewith certain embodiments. The apparatus 400 includes a chamber 418 witha pedestal 420, a shower head 414, and an in-situ plasma generator 416.The apparatus 400 also includes a system controller 422 to receive inputand/or supply control signals to various devices.

The etchant and, in certain embodiments, inert gases, such as argon,helium and others, are supplied to the remote plasma generator 406 froma source 402, which may be a storage tank. Any suitable remote plasmagenerator may be used for activating the etchant before introducing itinto the chamber 418. For example, a Remote Plasma Cleaning (RPC) units,such as ASTRON® i Type AX7670, ASTRON® e Type AX7680, ASTRON® ex TypeAX7685, ASTRON® hf-s Type AX7645, all available from MKS Instruments ofAndover, Mass., may be used. An RPC unit is typically a self-containeddevice generating weakly ionized plasma using the supplied etchant.Imbedded into the RPC unit a high power RF generator provides energy tothe electrons in the plasma. This energy is then transferred to theneutral etchant molecules leading to temperature in the order of 2000Kcausing thermal dissociation of these molecules. An RPC unit maydissociate more than 60% of incoming etchant molecules because of itshigh RF energy and special channel geometry causing the etchant toadsorb most of this energy.

In certain embodiments, an etchant is flown from the remote plasmagenerator 406 through a connecting line 408 into the chamber 418, wherethe mixture is distributed through the shower head 414. In otherembodiments, an etchant is flown into the chamber 418 directlycompletely bypassing the remote plasma generator 406 (e.g., the system400 does not include such generator). Alternatively, the remote plasmagenerator 406 may be turned off while flowing the etchant into thechamber 418, for example, because activation of the etchant is notneeded.

The shower head 414 or the pedestal 420 typically may have an internalplasma generator 416 attached to it. In one example, the generator 416is a High Frequency (HF) generator capable of providing between about 0W and 10,000 W at frequencies between about 1 MHz and 100 MHz. In a morespecific embodiment, the HF generator may deliver between about 0 W to5,000 W at about 13.56 MHz. The RF generator 416 may generate in-situplasma to enhance removal of the initial tungsten layer. In certainembodiments, the RF generator 416 is not used during the removaloperations of the process.

The chamber 418 may include a sensor 424 for sensing various processparameters, such as degree of deposition and etching, concentrations,pressure, temperature, and others. The sensor 424 may provideinformation on chamber conditions during the process to the systemcontroller 422. Examples of the sensor 424 include mass flowcontrollers, pressure sensors, thermocouples, and others. The sensor 424may also include an infra-red detector or optical detector to monitorpresence of gases in the chamber and control measures.

Deposition and selective removal operations generate various volatilespecies that are evacuated from the chamber 418. Moreover, processing isperformed at certain predetermined pressure levels the chamber 418. Bothof these functions are achieved using a vacuum outlet 426, which may bea vacuum pump.

In certain embodiments, a system controller 422 is employed to controlprocess parameters. The system controller 422 typically includes one ormore memory devices and one or more processors. The processor mayinclude a CPU or computer, analog and/or digital input/outputconnections, stepper motor controller boards, etc. Typically there willbe a user interface associated with system controller 422. The userinterface may include a display screen, graphical software displays ofthe apparatus and/or process conditions, and user input devices such aspointing devices, keyboards, touch screens, microphones, etc.

In certain embodiments, the system controller 422 controls the substratetemperature, etchant flow rate, power output of the remote plasmagenerator 406, pressure inside the chamber 418 and other processparameters. The system controller 422 executes system control softwareincluding sets of instructions for controlling the timing, mixture ofgases, chamber pressure, chamber temperature, and other parameters of aparticular process. Other computer programs stored on memory devicesassociated with the controller may be employed in some embodiments.

The computer program code for controlling the processes in a processsequence can be written in any conventional computer readableprogramming language: for example, assembly language, C, C++, Pascal,Fortran or others. Compiled object code or script is executed by theprocessor to perform the tasks identified in the program. The systemsoftware may be designed or configured in many different ways. Forexample, various chamber component subroutines or control objects may bewritten to control operation of the chamber components necessary tocarry out the described processes. Examples of programs or sections ofprograms for this purpose include process gas control code, pressurecontrol code, and plasma control code.

The controller parameters relate to process conditions such as, forexample, timing of each operation, pressure inside the chamber,substrate temperature, etchant flow rates, etc. These parameters areprovided to the user in the form of a recipe, and may be enteredutilizing the user interface. Signals for monitoring the process may beprovided by analog and/or digital input connections of the systemcontroller 422. The signals for controlling the process are output onthe analog and digital output connections of the apparatus 400.

Multi-Station Apparatus

FIG. 5A shows an example of a multi-station apparatus 500. The apparatus500 includes a process chamber 501 and one or more cassettes 503 (e.g.,Front Opening Unified Ports) for holding substrates to be processed andsubstrates that have completed processing. The chamber 501 may have anumber of stations, for example, two stations, three stations, fourstations, five stations, six stations, seven stations, eight stations,ten stations, or any other number of stations. The number of stations inusually determined by a complexity of the processing operations and anumber of these operations that can be performed in a sharedenvironment. FIG. 5A illustrates the process chamber 501 that includessix stations, labeled 511 through 516. All stations in the multi-stationapparatus 500 with a single process chamber 503 are exposed to the samepressure environment. However, each station may have a designatedreactant distribution system and local plasma and heating conditionsachieved by a dedicated plasma generator and pedestal, such as the onesillustrated in FIG. 4.

A substrate to be processed is loaded from one of the cassettes 503through a load-lock 505 into the station 511. An external robot 507 maybe used to transfer the substrate from the cassette 503 and into theload-lock 505. In the depicted embodiment, there are two separate loadlocks 505. These are typically equipped with substrate transferringdevices to move substrates from the load-lock 505 (once the pressure isequilibrated to a level corresponding to the internal environment of theprocess chamber 503) into the station 511 and from the station 516 backinto the load-lock 505 for removal from the processing chamber 503. Aninternal robot 509 is used to transfer substrates among the processingstations 511-516 and support some of the substrates during the processas described below.

In certain embodiments, one or more stations may be reserved for heatingthe substrate. Such stations may have a heating lamp (not shown)positioned above the substrate and/or a heating pedestal supporting thesubstrate similar to one illustrated in FIG. 4. For example, a station511 may receive a substrate from a load-lock and be used to pre-heat thesubstrate before being further processed. Other stations may be used forfilling high aspect ratio features including deposition and selectiveremoval operations.

After the substrate is heated or otherwise processed at the station 511,the substrate is moved successively to the processing stations 512, 513,514, 515, and 516, which may or may not be arranged sequentially. Themulti-station apparatus 500 is configured such that all stations areexposed to the same pressure environment. In so doing, the substratesare transferred from the station 511 to other stations in the chamber501 without a need for transfer ports, such as load-locks.

The internal robot 509 is used to transfer substrates between stations511-516. The robot 509 includes a fin with at least one arm for eachprocessing station (shown extending between stations). At the end of thearm adjacent to the processing stations are four fingers that extendfrom the arm with two fingers on each side. These fingers are used tolift, lower, and position a substrate within the processing stations.For example, in one embodiment, where the multi-station apparatusincludes six processing stations, the spindle assembly is a six armrotational assembly with six arms on one fin. For example, as shown inthe drawings the fin of the spindle assembly includes six arms, witheach arm having four fingers. A set of four fingers, i.e., two fingerson a first arm and two fingers on an adjacent, second arm, are used tolift, position and lower a substrate from one station to anotherstation. In this manner, the apparatus is provided with four fingers perpedestal, per station and per substrate.

In certain embodiments, one or more stations may be used to fillfeatures with tungsten-containing materials. For example, stations 512may be used for an initial deposition operation, station 513 may be usedfor a corresponding selective removal operation. In the embodimentswhere a deposition-removal cycle is repeated, stations 514 may be usedfor another deposition operations and station 515 may be used foranother partial removal operation. Section 516 may be used for the finalfilling operation. It should be understood that any configurations ofstation designations to specific processes (heating, filling, andremoval) may be used.

As an alternative to the multi-station apparatus described above, themethod may be implemented in a single substrate chamber or amulti-station chamber processing a substrate(s) in a single processingstation in batch mode (i.e., non-sequential). In this aspect of theinvention, the substrate is loaded into the chamber and positioned onthe pedestal of the single processing station (whether it is anapparatus having only one processing station or an apparatus havingmulti-stations running in batch mode). The substrate may be then heatedand the deposition operation may be conducted. The process conditions inthe chamber may be then adjusted and the selective removal of thedeposited layer is then performed. The process may continue with one ormore deposition-removal cycles and with the final filling operation allperformed on the same station. Alternatively, a single station apparatusmay be first used to perform only one of the operation in the new method(e.g., depositing, selective removal, final filling) on multiple wafersafter which the substrates may be returned back to the same station ormoved to a different station (e.g., of a different apparatus) to performone or more of the remaining operations.

Multi-Chamber Apparatus

FIG. 5B is a schematic illustration of a multi-chamber apparatus 520that may be used in accordance with certain embodiments. As shown, theapparatus 520 has three separate chambers 521, 523, and 525. Each ofthese chambers is illustrated with two pedestals. It should beunderstood that an apparatus may have any number of chambers (e.g., one,two, three, four, five, six, etc.) and each chamber may have any numberof chambers (e.g., one, two, three, four, five, six, etc.). Each chamber521-525 has its own pressure environment, which is not shared betweenchambers. Each chamber may have one or more corresponding transfer ports(e.g., load-locks). The apparatus may also have a shared substratehandling robot 527 for transferring substrates between the transferports one or more cassettes 529.

As noted above, separate chambers may be used for depositing tungstencontaining materials and selective removal of these deposited materialsin later operations. Separating these two operations into differentchambers can help to substantially improve processing speeds bymaintaining the same environmental conditions in each chamber. In otherwords, a chamber does not need to change its environment from conditionsused for deposition to conditions used for selective removal and back,which may involve different precursors, different temperatures,pressures, and other process parameters. In certain embodiments, it isfaster to transfer partially manufactured semiconductor substratesbetween two or more different chambers than changing environmentalconditions of these chambers.

Patterning Method/Apparatus:

The apparatus/process described hereinabove may be used in conjunctionwith lithographic patterning tools or processes, for example, for thefabrication or manufacture of semiconductor devices, displays, LEDs,photovoltaic panels and the like. Typically, though not necessarily,such tools/processes will be used or conducted together in a commonfabrication facility. Lithographic patterning of a film typicallycomprises some or all of the following steps, each step enabled with anumber of possible tools: (1) application of photoresist on a workpiece,i.e., substrate, using a spin-on or spray-on tool; (2) curing ofphotoresist using a hot plate or furnace or UV curing tool; (3) exposingthe photoresist to visible or UV or x-ray light with a tool such as awafer stepper; (4) developing the resist so as to selectively removeresist and thereby pattern it using a tool such as a wet bench; (5)transferring the resist pattern into an underlying film or workpiece byusing a dry or plasma-assisted etching tool; and (6) removing the resistusing a tool such as an RF or microwave plasma resist stripper.

Experimental

A series of experiments were conducted to determine effects of differentprocess conditions on selective removal of the deposited materials andresulting seam. It was found that increasing a substrate temperature andreducing an etchant flow rate can lead to mass-transport limited etchinginside the feature resulting in more material etched away near theopening than inside the feature.

In one experiment, different etching conditions and their effects onstep coverage were evaluated. Substrates with features that haveopenings of approximately 250 nanometers in cross-section and an aspectratio of approximately 10:1 were used. The features were first partiallyfilled with tungsten at about 395° C. substrate temperature, about 200sccm flow rate of the tungsten fluoride (WF₆) in argon and hydrogenenvironment. Several substrates were then cross-sectioned in order toanalyze tungsten distribution within the features. It was found that thelayer was slightly thinner inside the features (about 862 Angstromsthick on average) than around the openings (about 639 Angstroms thick onaverage) leading to step coverage of about 62%.

The remaining substrates were divided into two groups. Substrates in thefirst group were etched using reference process conditions: a chamberpressure of approximately 8 Torr, a substrate temperature ofapproximately 350° C., a flow rate of nitrogen tri-fluoride (NF3) ofapproximately 2,000 sccm, and etching duration of approximately 4seconds. Several substrates from this group were cross-sectioned afterthe etching to further analyze tungsten distribution within thefeatures. It was determined that the opening thickness (a thickness ofthe tungsten layer near the opening) was on average about 497 Angstroms,while the inside thickness was on average about 464 Angstroms, for astep coverage of about 107%.

The second group of wafers was etched using different (“improved”)process conditions. These new conditions were believed to push theetching inside the feature into the mass-transport limited regime and,thus, improve the step coverage even more. The substrate temperature wasincreased to approximately 395° C., while the etchant flow rate wasreduced to approximately 400 sccm. The etching was performed in achamber maintained at about 2 Torr for approximately 12 seconds. Theremaining etched layer was significantly thicker inside the features(about 555 Angstroms thick on average) than near the openings (about 344Angstroms thick on average). The calculated step coverage is about 161%.

FIG. 6A illustrates a schematic representation of a feature 601 providedin a partially manufactured semiconductor substrate 603 with atungsten-containing layer 605 formed with the feature 601 similar to theone used in the above experiment. The figure also specifies differentpoints of measurements of the layer thickness. FIG. 6B illustrates agraph of the thickness distribution of the tungsten-containing layer forthe experiment described above before etching and after etching for twodifferent process conditions. The horizontal axis of this graphcorresponds to the measuring points illustrated in FIG. 6A. Thicknessvalues provided in the graph are normalized to the respective values onthe field region (points 1 and 16). The bottom thin line 607 representsthickness distribution within the feature prior to any etching. Thisline indicates that the layer is generally slightly thinner inside thefeature than near the opening after deposition. The middle thick line609 represents thickness distribution for the substrates etched with thereference etching conditions. This distribution indicates slightlygreater step coverage than the one represented by the line 607. Finally,the top thin line 611 represents distribution of tungsten that wasetched using the “improved” conditions. It reveals substantiallyimproved step coverage. The thickness at the lowest (deepest) measuredpoints (points 8, 9, and 10, which were approximately 30-40% of thefeature's depth from the feature's bottom), is almost twice greater thanthe thickness near the field region (points 1, 2, 15, and 16).

CONCLUSION

Although the foregoing invention has been described in some detail forpurposes of clarity of understanding, it will be apparent that certainchanges and modifications may be practiced within the scope of theappended claims. It should be noted that there are many alternative waysof implementing the processes, systems and apparatus of the presentinvention. Accordingly, the present embodiments are to be considered asillustrative and not restrictive, and the invention is not to be limitedto the details given herein.

1. A method of filling a high aspect ratio feature provided on apartially manufactured semiconductor substrate, the method comprising:introducing a tungsten-containing precursor and a reducing agent into aprocessing chamber; depositing a layer of a tungsten-containing materialon the partially manufactured semiconductor substrate via a chemicalvapor deposition reaction between the tungsten-containing precursor andthe reducing agent, such that the layer partially fills the high aspectratio feature; introducing an activated etching material into theprocessing chamber; removing a portion of the layer using the activatedetching material to form a remaining layer; reintroducing thetungsten-containing precursor and the reducing agent into the processingchamber; and selectively depositing an additional layer of thetungsten-containing material on the partially manufactured semiconductorsubstrate via a chemical vapor deposition reaction between thetungsten-containing precursor and the reducing agent such that theadditional layer is thicker inside the feature than near the featureopening.